1. Field of the Invention
The present invention relates to a series of substituted N-phenyl-bipyrrolidine carboxamides. The compounds of this invention are modulators of H3 receptors and are, therefore, useful as pharmaceutical agents, especially in the treatment and/or prevention of a variety of diseases modulated by H3 receptors including diseases associated with the central nervous system. Additionally, this invention also relates to methods of preparation of substituted N-phenyl-bipyrrolidine carboxamides and intermediates therefor.
2. Description of the Art
Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. The physiological actions of histamine are mediated by four pharmacologically defined receptors (H1, H2, H3 and H4). All histamine receptors exhibit seven transmembrane domains and are members of the G-protein-coupled receptor superfamily (GPCRs).
The H1 receptor was the first member of the histamine receptor family to be pharmacologically defined, with the development of classical antihistamines (antagonists), such as diphenhydramine and fexofenadine. While antagonism of the H1 receptor of the immune system is commonly used for the treatment of allergic reactions, the H1 receptor is also expressed in various peripheral tissues and the central nervous system (CNS). In the brain, H1 is involved in the control of wakefulness, mood, appetite and hormone secretion.
The H2 receptor is also expressed in the CNS, where it may modulate several processes, including cognition. However, H2 receptor antagonists have primarily been developed to ameliorate gastric ulcers by inhibiting histamine-mediated gastric acid secretion by parietal cells. Classic H2 antagonists include cimetidine, ranitidine, and famotidine.
It should further be noted that H4 receptor function remains poorly defined, but may involve immune regulation and inflammatory processes.
H3 receptors have also been pharmacologically identified in the CNS, heart, lung, and stomach. The H3 receptor differs significantly from other histamine receptors, exhibiting low sequence homology (H1: 22%, H2: 21%, H4: 35%). H3 is a presynaptic autoreceptor on histamine neurons in the brain and a presynaptic heteroreceptor in nonhistamine-containing neurons in both the central and peripheral nervous systems. In addition to histamine, H3 also modulates the release and/or synthesis of other neurotransmitters, including acetylcholine, dopamine, norepinepherin and serotonin. Of particular note, presynaptic modulation of histamine release by H3 allows significant regulation of H1 and H2 receptors in the brain. Modulating multiple neurotransmitter signaling pathways, H3 may contribute to varied physiological processes. Indeed, extensive preclinical evidence indicates that H3 plays a role in cognition, sleep-wake cycle and energy homeostasis.
Modulators of H3 function may be useful in the treatment of obesity and central nervous system disorders (Schizophrenia, Alzheimer's disease, attention-deficit hyperactivity disorder, Parkinson's disease, depression, and epilepsy), sleep disorders (narcolepsy and insomnia), cardiovascular disorders (acute myocardial infarction), respiratory disorders (asthma), and gastrointestinal disorders. See generally, Hancock. Biochem. Pharmacol. 2006 Apr. 14; 71(8):1103-13 and Esbenshade et al. Mol. Interv. 2006 April; 6(2):77-88, 59.
Recently, compounds that are somewhat structurally related to the compounds of the present invention have been disclosed to be melanin concentrating hormone (MCH) receptor antagonists, see specifically U.S. Pat. No. 7,223,788. It should however be pointed out that there is no disclosure as to the activity of the compounds disclosed therein at the H3 receptor site.
All of the references described herein are incorporated herein by reference in their entirety.
Accordingly, it is an object of this invention to provide a series of substituted N-phenyl-bipyrrolidine carboxamides as selective H3 receptor ligands for treatment of H3 receptor regulated CNS disorders.
It is also an object of this invention to provide processes for the preparation of the substituted N-phenyl-bipyrrolidine carboxamides as disclosed herein.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed description that follows.